Radioactive Microsphere Technique Research Articles

The Physiology of Oxygen Transport by the Cardiovascular System: Evolution of Knowledge

The heart, vascular system, and red blood cells play fundamental roles in O2 transport. The fascinating research history that led to the current understanding of the physiology of O2 transport began in ancient Egypt in 3000 BC, when it was postulated that the heart was a pump serving a system of distributing vessels. Over 4 millennia elapsed before William Harvey (1578-1657) made the revolutionary discovery of blood circulation, but it was not until the 20th century that a lucid and integrative picture of O2 transport finally emerged. This review describes major research achievements contributing to this evolution of knowledge. These achievements include the discovery of the systemic and pulmonary circulations, hemoglobin within red blood cells and its ability to bind O2, and diffusion of O2 from the capillary as the final step in its delivery to tissue. The authors also describe the classic studies that provided the initial description of the basic regulatory mechanisms governing heart function (Frank-Starling law) and the flow of blood through blood vessels (Poiseuille's law). The importance of technical advances, such as the pulmonary artery catheter, the blood gas analyzer and oximeter, and the radioactive microsphere technique to measure the regional blood flow in facilitating O2 transport-related research, is recognized. The authors describe how religious and cultural constraints, as well as superstition-based medical traditions, at times impeded experimentation and the acquisition of knowledge related to O2 transport.

Do We have Enough Direct Evidence to Postulate that Abnormally Shaped Red Blood Cells Impair Microvascular Blood Flow in Critical Conditions?

abnormal RBCs were produced in-vitro but not as a result of a real critical condition. The conclusions received in these two studies were confirmed in “pure” in-vivo experiments by Machiedo et al. [18]. The authors performed exchange transfusion in rats with blood obtained animals rats subjected to trauma-hemorrhagic shock or to sham shock. The reduced RBC deformability in rats that experienced traumahemorrhagic shock and normal RBC deformability in those who were subjected to sham shock was confirmed by laser ektacytometry. However, the authors did not investigate RBC shape in transfused blood. It was demonstrated that microvascular blood flow in the lungs, spleen, and intestine measured by radioactive microsphere technique was significantly lower in rats subjected to the infusion of traumahemorrhagic shock blood than in those that were infused with sham blood.

Influence of intravenous infusion of ethanol on regional blood flow in conscious rats.

The effects of intravenous infusions of ethanol and saline (0.9% NaCl) on mean arterial pressure (MAP), heart rate (HR), total peripheral resistance (TPR), cardiac contractility (dP/dtmax) and systemic haemodynamics were studied in conscious, unrestrained rats by the radioactive microsphere technique. Saline (0.03 and 0.06 mL min-1 kg-1 for 12 min each dose) in the time-control group did not affect MAP, HR, TPR, dP/dtmax or vascular conductances in any organs or beds. While the low dose ethanol (2.4 mg min-1 kg-1) did not alter MAP, HR, TPR, systemic haemodynamics or dP/dtmax, the high dose (4.8 mg min-1 kg-1) slightly reduced MAP and TPR but did not affect HR, cardiac output or dP/dtmax. Both doses of ethanol vasodilated the intestine and spleen, but vasoconstricted the skin. The high dose caused additional vasodilatation in the heart and testes and the low dose also constricted the skeletal muscle bed. Our results show that ethanol, at non-hypotensive or slightly hypotensive doses, has marked vasodilator effects in the heart, intestine, spleen and testes.

The influence of methysergide on 5-hydroxytryptamine-induced changes in regional distribution of blood flow.

Systemic and regional haemodynamic variables were measured at the baseline and after saline or 5-HT infusions (5 microgram kg-1 min-1, i.v.) or methysergide injections (0.5 mg kg-1, i.v.). Cardiac output and its complete distribution were measured by the radioactive microsphere (15 micrometer diam) technique. Although 5-HT did not change the systemic variables, methysergide caused a moderate increase in systolic and mean blood pressure and heart rate. 5-HT caused a substantial increase in gastric and a moderate increase in cerebral and myocardial blood flow at the expense of that to the lungs (arteriovenous shunt + bronchial flows), kidneys and skin. While methysergide was able to reduce the vascular responses to 5-HT in stomach, skin, kidneys, heart, lungs and brain, the drug itself, like 5-HT, decreased the number of microspheres reaching the lungs. Since a large number of 15 micron microspheres can escape through the arteriovenous anastomoses to lodge in the lungs it seems likely that both 5-HT and methysergide can reduce the 'non-nutrient' flow through these anastomoses.

614 PLATELET COUNT IN CIRRHOSIS DEPENDS ON SPLEEN SIZE AND PERIPHERAL THROMBOPOIETIN, BUT NOT ON HEPATIC VENOUS PRESSURE GRADIENT

generation beta-blocker capable of increasing NO bioavailability on splanchnic and pulmonary hemodynamics in a cirrhotic rat model developing hepato-pulmonary syndrome (HPS). Methods: Male Sprague Dawley rats underwent bile duct ligation (BDL) to induce cirrhosis. The animals were orally treated with Nebivolol (NEBI; 10mg/kg) or vehicle (VEH) via feeding tube for seven days, starting three weeks after BDL, when cirrhosis was fully developed. 28 days after operation, heart rate (HR), mean arterial pressure (MAP), portal pressure (PP), and superior mesenteric artery blood flow (SMABF) were measured. Portosystemic collateral blood flow (PSCBF) and intrapulmonary shunting (IPS) were quantified by radioactive microsphere technique. Results: (Table-1): Body weight and MAP were similar in BDLVEH and BDL-NEBI rats, whereas HR was signficantly reduced by Nebivolol treatment. (p < 0.001). BDL-NEBI animals had significantly higher PP (p =0.005) and SMABF (p =0.016) than BDL-VEH animals. Nebivolol treatment did not affect IPS (p = 0.996).

Trauma-hemorrhagic shock-induced red blood cell damage leads to decreased microcirculatory blood flow*

To test the hypothesis that trauma-hemorrhagic shock (T/HS)-induced changes in red blood cells (RBC) contribute to the reduction of blood flow in distant organs. Laboratory study. Academic medical center laboratory. Specific pathogen-free male Sprague-Dawley rats weighing between 250 and 350 g. Rats were transfused with trauma-sham shock (T/SS), or T/HS whole blood, or RBC-depleted blood (blood with the RBC removed and consisting of white blood cells and plasma). Cardiac output and organ blood flow were measured by the radioactive microsphere technique. RBC tissue trapping, deformability, and RBC aggregation and adhesion were studied. Measurements of RBC adenosine triphosphate (ATP) and plasma fibrinogen were performed. Exchange transfusion with T/SS blood did not alter cardiac output or organ blood flow. However, cardiac output and blood flow in several organs were decreased when T/HS whole blood was used and RBCs were trapped in the organs that evidenced decreased blood flow. T/HS also increased RBC aggregation and adhesion, and decreased deformability. The ability of T/HS exchange transfusion to decrease microcirculatory blood flow did not appear to be due to plasma factors or non-RBC elements (i.e., white blood cell), because organ blood flow was not reduced after exchange transfusion with T/HS RBC-depleted blood. Likewise, neither decreased RBC ATP nor increased plasma fibrinogen explained the T/HS-induced changes that were observed. There was no change in fibrinogen levels during or after shock. Although there was a transient decrease in T/HS erythrocyte ATP levels during the early shock period, in contrast to RBC function, the ATP levels had returned to normal with resuscitation. T/HS induces significant changes in RBC functions and the injection of T/HS, but not T/SS, RBC leads to decreased organ blood flow. These findings confirm the hypothesis that T/HS-induced RBC alterations will directly cause organ hypoperfusion and suggest that T/HS-induced RBC damage contributes to this process. Thus, T/HS-induced changes in RBC function may contribute to the development of shock-induced multiple organ failure.

Altered vasodilator role of nitric oxide synthase in the pancreas, heart and brain of rats with spontaneous type 2 diabetes

Type 2 diabetes is associated with altered regional blood flow and expression of nitric oxide synthase (NOS). We examined the functional role of constitutive and inducible NOS synthase (cNOS and iNOS, respectively) on regional blood flow in thiobutabarbital-anesthetized Zucker diabetic fatty (ZDF) and control rats via the radioactive microspheres technique. Blood flow was measured at baseline (1 h after surgery), after i.v. administration of 1400W ( N-3-aminomethyl-benzyl-acetamidine, selective iNOS inhibitor, 3 mg/kg), and again after i.v. N G-nitro- l-arginine methyl ester ( l-NAME, non-selective NOS inhibitor, 8 mg/kg). Both groups had similar baseline mean arterial pressure, cardiac output and total peripheral resistance, but the ZDF rats had lower heart rate relative to the control rats (272 versus 305 beats/min). Whereas 1400W did not alter mean arterial pressure or blood flow in either group, l-NAME markedly increased mean arterial pressure and total peripheral resistance, and reduced cardiac output, heart rate, blood flow and arterial conductance in all organs/tissues of both the control and ZDF rats. l-NAME caused greater vasoconstriction in the heart (1.5-times the constriction in control rats) and brain (1.5-times) of the ZDF rats, but less in the pancreas (0.6-times). Thus, cNOS had greater vasodilator control of the heart and brain, but less in the pancreas of the ZDF than control rats. iNOS has negligible influence on blood flow in both groups of rats.

Vascular actions of the prostacyclin receptor antagonist BAY 73-1449 in the portal hypertensive rat

We have investigated the actions of the postacyclin receptor antagonist BAY 73-1449 on shunt vessel development and shunt flow in the portal vein ligated portal hypertensive Wistar rat in vivo. BAY 73-1449 (0.1–1 mg/kg), given intravenously, did not significantly reduce mesenteric inflow, but significantly reduced splenic shunt vessel outflow, compared to the effects of vehicle, in anaesthetized portal vein ligated rats as measured by shunt vessel conductance. There were no differences between portal vein ligated animals treated, beginning just before portal vein ligation, with vehicle for 7 days and animals treated for 7 days with BAY 73-1449 (1–5 mg/kg, s.c.) in the degree of porto-systemic shunting, as measured by the radioactive microsphere technique in anaesthetized rats. Portal pressure was similar in animals treated with vehicle or BAY 73-1449. It is concluded that the prostacyclin receptor antagonist BAY 73-1449 can acutely reduce shunt vessel blood flow in portal hypertensive rats.

The Physiology of Bone Blood Flow: A Review

Bone circulation plays an important role in bone physiology, but has been relatively poorly studied, because most techniques of circulatory research are difficult to apply to bone. This article summarizes briefly some of the important aspects of the physiology of bone blood flow most relevant to orthopaedics. The gold standard for experimental measurement of bone blood flow is the radioactive microsphere technique, though advances are being made in other techniques, such as positron emission tomography, laser and ultra-sound Doppler velocimetry, and near infrared spectroscopy, that may provide useful clinical measurement in the future. Multiple vascular pathways contribute to an adaptive response to traumatic disruption of bone circulation. The microcirculation is not merely a passive conduit for blood flow, but plays an active role in controlling bone processes such as osteochondral ossification. The pathophysiology of bone circulation has been associated with osteonecrosis, but more and more evidence is pointing to the importance of bone circulation in fracture repair and osteoporosis, both of which are potentially very exciting areas for future studies.

Ligustrazine alleviates acute renal injury in a rat model of acute necrotizing pancreatitis

To evaluate the effect of ligustrazine, a traditional Chinese medicine, on renal injury in a rat model of acute necrotizing pancreatitis (ANP). A total of 192 rats were randomly divided into three groups: control (C group), ANP without treatment (P group), and ANP treated with ligustrazine (T group). Each group was further divided into 0.5, 2, 6, 12 h subgroups. All rats were anesthetized with an intraperitoneal injection of sodium pentobarbital. Sodium taurocholate was infused through the pancreatic membrane to induce ANP. T group was infused sodium taurocholate as above, and 0.6% ligustrazine was then administered via the femoral vein. Serum urea nitrogen (BUN) and creatinine (Cr) concentrations were measured for the evaluation of renal function. The effects of ligustrazine on the severity of renal injury were assessed by renal function, TXA(2)/PGI(2) and histopathological changes. Renal blood flow was determined by the radioactive microsphere technique (RMT). Compared with control group, the renal blood flow in P group was decreased significantly. Serious renal and pancreatic damages were found in P group, the BUN and Cr levels were elevated significantly, and the ratio of TXA(2) to PGI(2) was increased at 2, 6 and 12 h. Compared with P group, the blood flow of kidney was elevated significantly at 6 and 12 h after induction of ANP, the renal and pancreatic damages were attenuated, and the BUN and Cr levels were decreased significantly, and the ratio of TXA(2) to PGI(2) was decreased at 6 and 12 h in T group. Microcirculatory disorder (MCD) is an important factor for renal injury in ANP. Ligustrazine can ameliorate the condition of MCD and the damage of pancreas and kidney.

Comparison of Neutron Activated and Radiolabeled Microsphere Methods for Measurement of Transmural Myocardial Blood Flow in Dogs

The 'gold standard' radioactive microsphere (RM) technique for measurement of organ blood flow under various experimental conditions is inaccessible to many researchers due to increasing environmental concerns regarding safety and disposal of low-level radioactive waste materials. A new method using neutron activated microspheres (NAM) has recently been described. We compared regional myocardial blood flows using the new formulation STERIspheres (NAM; 15.0 +/- 0.1 [SD] microm; density 1.5 gr/mL) with RM (15.0 +/- 0.1 [SD] microm; density 1.5 gr/mL) under different experimental conditions during acute ischemia-reperfusion injury in dogs. Random paired combinations of four different RM and NAM were co-injected into the left atrium during autoregulation, coronary occlusion and flow-mediated hyperemia (reperfusion) in the same animal. The left ventricle was divided into non-ischemic and ischemic regions and further subdivided into endocardial, mid-myocardial and epicardial portions. After gamma-counting, blood and myocardial tissue samples (n = 180) were dried and then shipped to a core facility for neutron activation and analysis. NAM-RM blood flow data were directly compared by ANOVA and regression analysis; Bland and Altman analysis was also performed to assess mean differences in blood flow with NAM-RM. A direct relation for blood flow between NAM-RM was observed; the slope of the relation (1.17 RM +/- 0.04 [SEE]) was different from unity but the intercept (0.06 +/- 0.06 [SEE]) was not different from the origin. Intermethod mean differences were minimal between NAM-RM in the low to normal range of blood flow and were increased at the higher blood flow levels the latter being of minor physiological consequence. A direct relation for endo/epicardial blood flow ratios between NAM-RM was also observed; the slope of the relation (0.98 RM +/- 0.04 [SEE]) and the intercept (0.03 +/- 0.06 [SEE]) were not different from unity or the origin, respectively. RESULTS show that in addition to limiting production of radioactive waste materials, NAM accurately measure myocardial blood flow, endocardial/epicardial and ischemic/non-ischemic blood flow distributions over a wide range. We compared myocardial blood flows using paired combinations of neutron activated (NAM) and the 'gold standard' radiolabeled microspheres (RM) co-injected during autoregulation, coronary occlusion and flow-mediated hyperemia in an in situ canine ischemia-reperfusion preparation. A direct relation for blood flow and endo/epicardial blood flow ratios between NAM-RM was observed; intermethod mean differences between NAM-RM were minimal in the low to normal blood flow range but increased at higher blood flow levels. These results indicate that NAM accurately measure myocardial blood flow and its transmural distribution in addition to limiting unnecessary production of radioactive laboratory waste products.

Role of PGI2in the formation and maintenance of hyperdynamic circulatory state of portal hypertensive rats

To investigate the role of prostacyclin (PGI(2)) and nitric oxide (NO) in the development and maintenance of hyperdynamic circulatory state of chronic portal hypertensive rats. Ninety male Sprague-Dawley rats were divided into three groups: intrahepatic portal hypertension (IHPH) group by injection of CCl(4), prehepatic portal hypertension (PHPH) group by partial stenosis of the portal vein and sham-operation control (SO) group. One week after the models were made, animals in each group were subdivided into 4 groups: saline controlled group (n = 23), Nomega-nitro-L-arginine (L-NNA) group (n = 21) group, indomethacin (INDO) group (n = 22) and high-dose heparin group (n = 24). The rats were administrated 1 mL of saline, L-NNA (3.3 mg/kg.d) and INDO (5 mg/kg.d) respectively through gastric tubes for one week, then heparin (200 IU/Kg/min) was given to rats by intravenous injection for an hour. Splanchnic and systemic hemodynamics were measured using radioactive microsphere techniques. The serum nitrate/nitrite (NO(2)(-)/NO(3)(-)) levels as a marker of production of NO were assessed by a colorimetric method, and concentration of 6-keto-PGF1alpha, a stable hydrolytic product of PGI(2), was determined by radioimmunoassay. The concentrations of plasma 6-keto-PGF1alpha (pg/mL) and serum NO(2)(-)/NO(3)(-) (micromol/L) in IHPH rats (1123.85+/-153.64, 73.34+/-4.31) and PHPH rats (891.88+/-83.11, 75.21+/-6.89) were significantly higher than those in SO rats (725.53+/-105.54, 58.79+/-8.47) (P<0.05). Compared with SO rats, total peripheral vascular resistance (TPR) and spanchnic vascular resistance (SVR) decreased but cardiac index (CI) and portal venous inflow (PVI) increased obviously in IHPH and PHPH rats (P<0.05). L-NNA and indomethacin could decrease the concentrations of plasma 6-keto-PGF1alpha and serum NO(2)(-)/NO(3)(-) in IHPH and PHPH rats (P<0.05). Meanwhile, CI, FPP and PVI lowered but MAP, TPR and SVR increased (P<0.05). After deduction of the action of NO, there was no significant correlation between plasma PGI(2) level and hemodynamic parameters such as CI, TPR, PVI and SVR. However, after deduction of the action of PGI(2), NO still correlated highly with the hemodynamic parameters, indicating that there was a close correlation between NO and the hemodynamic parameters. After administration of high-dose heparin, plasma 6-keto-PGF(1alpha) concentrations in IHPH, PHPH and SO rats were significantly higher than those in rats administrated vehicle (P<0.05). On the contrary, levels of serum NO(2)(-)/NO(3)(-) in IHPH, PHPH and SO rats were significantly lower than those in rats administrated Vehicle (P<0.05). Compared with those rats administrated vehicle, the hemodynamic parameters of portal hypertensive rats, such as CI and PVI, declined significantly after administration of high-dose heparin (P<0.05), while TPR and SVR increased significantly (P<0.05). It is NO rather than PGI(2) that is a mediator in the formation and maintenance of hyperdynamic circulatory state of chronic portal hypertensive rats.

Alcohol ingestion before burn injury decreases splanchnic blood flow and oxygen delivery.

Recent studies from our laboratory have shown that alcohol and burn injury impair intestinal barrier and immune functions. Although multiple factors can contribute to impaired intestinal barrier function, such an alteration could result from a decrease in intestinal blood flow (BF) and oxygen delivery (DO2). Therefore, in this study, we tested the hypothesis that alcohol ingestion before burn injury reduces splanchnic blood flow and oxygen delivery. Rats (250 g) were gavaged with alcohol to achieve a blood ethanol level in the range of 100 mg/dl before burn or sham injury (25% total body surface area). Day 1 after injury, animals were anesthetized with methoxyflurane. Blood pressure, cardiac output (CO), +/-dP/dt, organ BF (in ml.min(-1).100 g(-1)), and DO2 (in mg.ml(-1).100 g(-1)) were determined. CO and organ BF were determined using a radioactive microsphere technique. Our results indicate that blood pressure, CO, and +dP/dt were decreased in rats receiving a combined insult of alcohol and burn injury compared with rats receiving either burn injury or alcohol alone. This is accompanied by a decrease in BF and DO2 to the liver and intestine. No significant change in BF to the coronary arteries (heart), brain, lung, skin, and muscles was observed after alcohol and burn injury. In conclusion, the results presented here suggest that alcohol ingestion before burn injury reduces splanchnic BF and DO2. Such decreases in BF and DO2 may cause hypoxic insult to the intestine and liver. Although a hypoxic insult to the liver would result in a release of proinflammatory mediators, a similar insult to the intestine will likely perturb both intestinal immune cell and barrier functions, as observed in our previous study.

Commentary

HIGHLIGHTED TOPICSSkeletal and Cardiac Muscle Blood FlowCommentaryGary C. SieckGary C. SieckJournal of Applied Physiology September 2004, Volume 97Published Online:01 Sep 2004https://doi.org/10.1152/japplphysiol.00635.2004MoreSectionsPDF (9 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Reactive oxygen species are generally thought to play a role only in pathological conditions. However, recent studies have suggested that reactive oxygen species may play a physiological role in the modulation of vascular tone. In the first featured article, entitled “Biphasic effect of hydrogen peroxide on skeletal muscle arteriolar tone via activation of endothelial and smooth muscle signaling pathways,” Dr. C. Cseko and colleagues (1) examined the role of H2O2 in local regulation of skeletal muscle blood flow. These investigators provide further evidence supporting concentration-dependent effects of H2O2 on vasomotor tone of arterioles mediated by prostanoids, nitric oxide, and potassium channels. The findings of this study are important because in various physiological and/or pathological conditions, endothelial or smooth muscle cells may release H2O2 during increased oxidative metabolism. Under physiological conditions, H2O2 may provide a feedback signal to locally couple tissue metabolism to blood supply. Under pathological conditions, circulating leukocytes or macrophages that are in or near the vascular wall may produce significant amounts of H2O2, which may then modulate arteriolar diameter and locally increase blood flow, thereby ensuring that all necessary components of inflammation are present in the microcirculation. Together, these findings emphasize that the role of reactive oxygen species, such as H2O2, should be considered when attempting to explain the multifactorial nature of local regulation of blood flow.In the second featured article, entitled “Downhill running: a model of exercise hyperemia in the rat spinotrapezius muscle,” Dr. Y. Kano and colleagues (2) hypothesized that downhill treadmill running recruits the spinotrapezius muscle, as evidenced by the exercise hyperemia. Investigating the processes of blood-muscle exchange requires in vivo observations of capillary hemodynamics via intravital microscopy techniques. Visualization with transmission light microscopy requires that muscle tissue possess excellent optical properties and can be accessed without disturbing neural or vascular supplies. These criteria limit the selection of candidate muscles and impose a difficult challenge to investigation of microvascular adaptations to exercise training. The validity of swimming and uphill and flat running protocols used to train the cremaster and spinotrapezius muscles, respectively, has been questioned on the basis of their effectiveness in inducing physiological hyperemia. In a rat model, these investigators used radioactive microsphere techniques and demonstrated an approximate threefold increase in spinotrapezius blood flow during downhill running. These findings provide a physiological paradigm for the investigation of the microcirculatory basis of enhanced blood-muscle exchange and muscle performance after training.REFERENCES1 Cseko C, Bagi Z, and Koller A. Biphasic effect of hydrogen peroxide on skeletal muscle arteriolar tone via activation of endothelial and smooth muscle signaling pathways. J Appl Physiol 97: 1130–1137, 2004.Google Scholar2 Kano Y, Padilla D, Hageman KS, Poole DC, and Musch TI. Downhill running: a model of exercise hyperemia in the rat spinotrapezius muscle. J Appl Physiol 97: 1138–1142, 2004.Google Scholar Download PDF Previous Back to Top Next FiguresReferencesRelatedInformation More from this issue > Volume 97Issue 3September 2004Pages 1129-1129 Copyright & PermissionsCopyright © 2004 the American Physiological Societyhttps://doi.org/10.1152/japplphysiol.00635.2004History Published online 1 September 2004 Published in print 1 September 2004 Metrics

Spinal blood flow in 24-hour megadose glucocorticoid treatment in awake pigs

Because of the controversy regarding the benefits of 24-hour administration of methylprednisolone in patients with spinal cord injury (SCI), it is important to investigate its mechanism of action and side effects. This study was conducted to determine if high-dose methylprednisolone modulates neural and vertebral blood flow in an awake large-sized animal model without SCI. From a group of 18 immature female domestic pigs born to nine different litters, nine animals were randomly allocated to receive methylprednisolone treatment, whereas their nine female siblings served as controls. Drug or placebo was applied in a blinded fashion by a third person not involved in the study. The following treatment for SCI, as suggested by the North American Spinal Cord Injury Study, was administered to the awake pig: methylprednisolone (30 mg/kg of body weight) was infused into the jugular vein during a 15-minute period, followed by a 45-minute pause, and the infusion was maintained over a 23-hour period at a dose of 5.4 mg/kg body weight/hour. By means of the radioactive tracer microsphere technique, spinal cord blood flow (SCBF) was measured in the awake standing pig in the cerebrum, and in spinal gray and white matter, nerve roots, endplates, cancellous bone, cortical shell, and T12-L2 discs. Blood flow was measured before, 1 hour after initiation of infusion, and 24 hours postinfusion. Examination of blood flow in the neural and vertebral tissue samples, as well as of central hemodynamics, revealed no significant difference between the experimental and control groups, and this parity was maintained throughout the experimental phases. In the awake pig model, 24-hour methylprednisolone treatment does not modulate cerebral or SCBF, nor does it increase the risk for vertebral osteonecrosis by producing vertebral ischemia.

Comparison of Cardioprotective Efficacy of Two Thromboxane A2 Receptor Antagonists

The purpose of the current study was to compare the efficacy of two structurally unrelated thromboxane A (TXA ) receptor antagonists, KT2-962 and daltroban (BM 13.505), in a dog model of myocardial ischemia/reperfusion injury. Pentobarbital-anesthetized dogs were subjected to left circumflex coronary artery occlusion for 90 minutes followed by 5 hours of reperfusion. Vehicle, KT2-962 (10 mg/kg), or daltroban (10 mg/kg) were administered as intravenous boluses 10 minutes before coronary occlusion. Systemic hemodynamics were measured throughout the experiments and regional myocardial blood flow was measured by the radioactive microsphere technique. At the end of the reperfusion period, myocardial infarct size was quantified by staining with triphenyltetrazolium chloride. Neither KT2-962 nor daltroban significantly altered heart rate, mean arterial blood pressure, or regional myocardial blood flow. The content of myeloperoxidase activity in the ischemic/reperfused tissue, an index of neutrophil infiltration, was not significantly different among the three treatment groups. However, administration of KT2-962, but not daltroban, significantly reduced the incidence of ventricular fibrillation during the ischemic period and significantly reduced myocardial infarct size expressed as a percentage of the risk region (approximately 40%). Subsequent in-vitro assays using electron spin resonance spectroscopy demonstrated that KT2-962 inhibited the formation of hydroxyl radicals, whereas daltroban had no effect. These results suggest that the beneficial effects of KT2-962 may be due to its direct free radical scavenging properties rather than its ability to block TXA receptors.(2) (2) (2)

Acute adenosine treatment is effective in augmentation of ischemic tolerance in muscle flaps in the pig: an update.

The objective of the present project was to investigate the efficacy and mechanism of acute (10-minute) adenosine treatment for augmentation of ischemic tolerance in muscle flaps in pigs. Varying doses of adenosine were infused into 28 latissimus dorsi muscle flaps through the axillary artery (0, 0.5, or 2.0 mg per flap) and 22 gracilis muscle flaps through the medial circumflex femoral artery (0, 10, or 20 mg per flap) over 10 minutes. Ten minutes after adenosine infusion, these muscle flaps were subjected to 4 hours of sustained warm global ischemia. In addition, one group of latissimus dorsi muscle flaps (n = 6) received a 10-minute intraarterial adenosine infusion (0.5 mg) at the beginning of reperfusion. Muscle biopsies (n = 4 or 5) for adenosine triphosphate (ATP) analysis were obtained before and after adenosine infusion and at the end of 4 hours of ischemia. The extent of muscle infarction was assessed at 48 hours of reperfusion by the tetrazolium dye staining technique. Muscle blood flow in latissimus dorsi muscle flaps was measured at the end of adenosine infusion (0 or 0.5 mg per flap, n = 8) by the radioactive microsphere (15-microns) technique. It was observed that adenosine, at all doses tested, significantly (p < 0.05) reduced the extent of muscle infarction in latissimus dorsi muscle flaps (control, 40.3 +/- 2.2 percent; 0.5 mg, 20.6 +/- 1.6 percent; 2.0 mg, 18.2 +/- 1 percent) and gracilis muscle flaps (control, 31.0 +/- 1.5 percent; 10 mg, 14.3 +/- 3 percent; 20 mg, 11.6 +/- 1.2 percent). Preischemic adenosine treatment (0.5 mg per flap) was associated with maintenance of a significantly (p < 0.05) higher muscle content of ATP in latissimus dorsi muscle flaps at the end of 4 hours of ischemia compared with saline-treated ischemic controls. Postischemic adenosine treatment did not protect latissimus dorsi muscle flaps against infarction. Furthermore, adenosine treatment did not have any significant effect on mean systemic arterial blood pressure or muscle blood flow in latissimus dorsi muscle flaps. It is concluded that acute (10-minute) preischemic adenosine treatment is effective in augmentation of ischemic tolerance in muscle flaps and that this protective effect of adenosine may be, at least in part, the result of slowing muscle ATP depletion during sustained ischemia. The possible mechanisms of this adenosine-induced energysparing effect are discussed.

Plasma taurine concentrations increase after enteral glutamine supplementation in trauma patients and stressed rats

Taurine is a unique amino acid with antioxidant and osmolytic properties. Glutamine serves as the preferred fuel for the gut, liver, and immune cells and as a precursor for antioxidants. Trauma patients have low glutamine concentrations. We investigated the effect of glutamine-enriched enteral nutrition on plasma taurine concentrations in patients with severe trauma (injury severity score >20). Additionally, plasma taurine concentrations and organ fluxes were studied in a stressed rat model. Twenty-nine patients with multiple trauma received glutamine-enriched nutrition and 31 patients received isocaloric, isonitrogenous control solution for 5 d. Plasma taurine and glutamine concentrations were measured. Male Wistar rats (250-300 g) received a glutamine-enriched diet (12%, by wt) or a control solution for 2 wk. Plasma taurine concentrations were measured. Taurine fluxes and fractional extraction rates in the liver, kidneys, and gut were assessed with a radioactive microsphere technique. Both patient groups had low taurine concentrations on day 1. From day 3 onward, the glutamine-fed patients had significantly higher taurine concentrations. Rats fed a glutamine-enriched diet had significantly higher plasma taurine concentrations than did the controls. A high taurine uptake was found in the liver, kidneys, and gut of the glutamine-fed rats. Fractional extraction rates were not significantly different between the rat groups. Glutamine enrichment increases plasma taurine in trauma patients and in stressed rats. Because of increased availability, organ fluxes showed a higher taurine uptake in the liver, kidneys, and gut. The reduction in morbidity with glutamine enrichment could be explained in part by increased taurine availability.

Locomotor Activity and Temperature Rhythms in Cirrhotic and Portal Hypertensive Rats

This study was performed to examine the circadian variations in body temperature and locomotor activity in two rat models of liver damage and portal-systemic collateralization, it is, cirrhosis by common bile duct ligature and portal vein ligation. Locomotor activity and temperature were measured telemetrically, and the degree of portal-systemic shunting was evaluated by the radioactive microsphere technique. In cirrhotic rats a significant increase in portal pressure and portal-systemic shunting occurred, with extensive liver damage and ascitis. These changes were accompanied by a derangement of the activity rhythm (decrease in total activity, night/day ratio and Qp) and an increase in the amplitude of the temperature rhythm. In portal vein-ligated rats, portal vein pressure and portal-systemic shunting increased significantly, with no changes in any of the rhythm parameters analyzed (total, diurnal and nocturnal activity pulses, night/day activity ratio and Qp for activity; mesor, amplitude and free-running period for temperature). The results indicate that liver dysfunction, and not merely portal hypertension or portal-systemic shunting, is the main factor affecting daily rhythms in cirrhotic rats.

Evidence for the involvement of ET B receptors in ET-1-induced changes in blood flow to the rat breast tumor

Structure, growth, and function of the blood vessels in breast tumors are markedly different from those in normal breast tissue due to changes in the production of growth factors such as vascular endothelial growth factor (VEGF), vasoactive substances such as endothelin-1 (ET-1) and cytokines. The role of ET-1 in breast tumor angiogenesis is not adequately understood. Studies have shown that the expression of proET-1, proET-3, and ET(B) receptors is increased in breast tumor. However, it is unclear whether there are any changes in ET-1-induced vascular responses in breast tumor. Hence, in the present study we investigated systemic hemodynamics and regional circulatory effects of ET-1 in rats with breast tumors. Female Sprague-Dawley rats weighing 180-200 g were divided into the following groups: (1) normal rats treated with saline ( n=6), (2) tumor-bearing rats treated with methylnitrosourea (MNU) ( n=6), (3) normal rats treated with saline plus the specific ET(B) receptor antagonist BQ 788 ( n=5), and (4) tumor-bearing rats treated with MNU plus BQ 788 ( n=5). Tumor development was monitored by regular palpation and measurement of tumor size. Once tumors had reached approximately 2-4 cm in diameter, the rats were anesthetized with urethane (1.5 g/kg i.p.) and their cardiovascular parameters were measured using a radioactive microsphere technique. Simultaneously, blood perfusion to the breast tissue was also measured using a laser Doppler technique. ET-1 produced a significant increase in mean arterial pressure in normal and tumor-bearing rats. Blood flow to the tumor tissue increased significantly in response to ET-1 as compared to breast tissue in normal rats. This response was accompanied by a concomitant decrease in vascular resistance in the tumor tissue. These results were confirmed by laser Doppler flowmetry, which showed a significant increase in blood perfusion to breast tumor compared to normal breast tissue. This increase in blood perfusion was attenuated by pretreatment with BQ 788, suggesting an ET(B) receptor-mediated vasodilator action of ET-1 in rat breast tumor. The results indicate that ET-1 induced an increase in blood flow to breast tumor tissue mediated through ET(B) receptors.